The invention relates to an inductive switch apparatus having a sensor unit and can be used in particular for a position switch apparatus that is used in automatic motor vehicle transmissions.
Known in the prior art is a displacement and angle sensor, in particular for determining a gear that has been selected in the motor vehicle field, in accordance with patent DE 198 06 529. The known displacement and angle sensor has four measurement coils that are arranged at right angles to one another on a coil carrier in an X/Y plane and are connected to evaluation electronics. The sensor has a so-called target that can be moved largely parallel to the X/Y plane relative to the measurement coils, thereby inducing voltages in the measurement coils. The evaluation electronics can determine the path traveled in the Y direction and the angle α of the target in a Z/X plane from the induced voltages. The known displacement and angle sensor is distinguished in that the opposing measurement coils are arranged spaced from one another and the adjacent measurement coils at least partially overlap one another.
The older application DE 102 42 385 A1 discloses an inductive sensor unit having at least two sensor coils that are mounted on a printed circuit board adjacent to one another in a planar manner. By an adjacent conductive actuating element the distance x to the sensor coils and the overlap y of the sensor coils can be changed. The evaluation of the changes in inductance that thus arise occurs, as for inductive proximity switches, by including the sensor coils in an oscillating circuit. Such an evaluation of resonance is sensitive to temperature and relatively complex.
Furthermore known in the field of automobiles is widespread employment of mechanical switches, including lock systems, operating elements for the dashboard, seat adjustments, mirror adjustments, etc. Mechanical switches have the disadvantage that they do not work in a wear-free manner. Their service life is limited by the material wear of the contact material, changes in the material (oxidation), and deposits on the switch contacts due to mechanical friction or electrical overloading or due to arcing when turning off.
One particular form of mechanical switches are mechanical sliding switches. A displaceable contact runs over a slide track and thus, depending on the position, produces a contact to various connections (so-called encoding switches). In such a shift gate unit, vibrations that occur in the vehicle lead to increased wear in the sliding contacts and slide tracks.
In modern vehicles, actuating motors these days are generally switched via wear-free power semiconductors, which then however are controlled by non-wear-free switches. In order to design the system completely wear-free, it is necessary to develop novel switches that work without mechanical switch contacts (that is, with sensors).
Known from the prior art are Hall sensors that react to the approach of permanent magnets and thus trigger a switching function. Furthermore known is the use of GMR sensors, which are based on the effect of a change in resistance that is caused by an external magnetic field. The external magnetic field can derive from a permanent magnet or a magnetizable plastic and can initiate appropriate switching functions.
Furthermore known is the use of light barriers and reflex light barriers, which have the disadvantage that they are sensitive to stray light and that the optical components age and can be soiled easily. The use of such sensors furthermore has the disadvantage that they are expensive compared to mechanical switches and inductive switches.
In switching elements, cost-effective printed circuit boards are frequently used as carriers for illumination, displays, or mechanical switches. The presence of such a printed circuit board favors the use of the present invention. The working principle of the inductive coupling of two sensor coils applied to the printed circuit board and their damping by a conductive actuator was disclosed as a cost-effective option for instance in DE 101 25 278. In it, damping strength correlates to the position of the actuator relative to the sensors. In this technology, it can be disadvantageous that the sensors in their practical design must have a minimum size of approx. 10 mm×10 mm on the printed circuit board so that acceptable coupling can be achieved and thus the electronics can be designed simply and cost-effectively. In the printed circuit boards that can currently be economically produced, a local resolution of 0.12 mm is attained, i.e., the conductor width of the sensor windings can be a maximum of 0.12 mm, just like the insulating width between the windings. As a result of this, the transmitter coil and the receiver coil of the sensors can have only approx. 5 windings.
The object of the invention is to influence the inductance of sensor coils using an actuator brought over the coil and to evaluate this change in inductance in a simple manner.